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On the stress-strain alignment in premixed turbulent flames
Umair Ahmed1, Nilanjan Chakraborty2, Markus Klein3
1School of Engineering, Newcastle University, Newcastle Upon-Tyne, NE1 7RU, UK. umair.ahmed@newcastle.ac.uk.
Scientific Reports
|March 27, 2019
Summary
Investigating sub-grid scale stresses in turbulent premixed flames reveals their alignment with the resolved strain rate shifts across the flame brush. This change, dependent on turbulence intensity, impacts large eddy simulation modeling.
Area of Science:
- Fluid Dynamics
- Combustion Science
- Computational Science
Background:
- Turbulent flows involve interactions between large and small structures, crucial for energy transfer.
- Large Eddy Simulation (LES) requires parameterizing small-scale structure responses to resolved large scales.
- Premixed flames complicate LES due to heat release influencing unresolved turbulence-chemistry interactions.
Purpose of the Study:
- To investigate the influence of sub-grid scale (SGS) stresses on the kinetic energy budget in turbulent premixed flames.
- To analyze the alignment between SGS stresses and the resolved strain rate across the flame brush.
Main Methods:
- Utilized a direct numerical simulation (DNS) database of statistically planar premixed flames.
- Subjected flames to forced isotropic turbulence.
- Analyzed the alignment of eigenvectors of SGS stresses and the resolved strain rate.
Main Results:
- Found that the alignment between SGS stress eigenvectors and resolved strain rate eigenvectors changes across the flame brush.
- Demonstrated this alignment change is dependent on the flame's turbulence intensity.
- Observed variations with different turbulence intensities and filter widths.
Conclusions:
- The alignment of sub-grid scale stresses with the resolved strain rate is not constant in turbulent premixed flames.
- This variability, influenced by turbulence levels, has significant implications for sub-grid scale modeling in LES of combustion.
- Further research is needed to refine SGS models accounting for these dynamic alignments.
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